1. Field of the Invention
The present invention relates to electrolysis cells and their operation. More particularly, the invention pertains to the operation of electrolysis cells under conditions of varying power input.
2. Description of the Prior Art
By way of background, an electrolysis cell has electrochemical properties that allow for the conversion of electrical energy into chemical energy. For example, water, in the form of steam, can be converted into hydrogen and oxygen when electrical energy is applied to the cell. As the electrical energy passes through the cell, the electrical resistance of the materials that make up the cell cause some of the electrical energy to be converted into heat (thermal energy). This thermal energy can be used in the electrolysis reaction. As the supplied electrical energy increases, a point is reached where the thermal energy generated within the cell and the supplied electrical energy equals the energy required to complete the reaction. This is called the thermal neutral voltage (Vtn).
For typical applications where the amount of available electrical power (i.e., energy rate) is constant, an electrolysis cell can be designed to run at Vtn. However, for applications where the electrical power is changing over time, as is the case for some renewable energy sources (e.g., wind turbines, solar panels, etc.), changes to cell operating conditions will occur. A specific electrolysis cell will have a defined voltage-current (electrical power) curve. Therefore, if no other operating parameters change, as the input electrical power changes, both the voltage and the current must change. The result is that the electrolysis cell may not always be operating at Vtn. If the electrical power increases, the voltage will exceed Vtn, causing excess heat to be generated in the electrolysis cell that must be removed. If the electrical power decreases, the voltage will be less than Vtn, and heat must be added to complete the reaction. Although there are methods to add additional heat or to remove excess heat, all such methods result in a thermal gradient in the cell. Thermal gradients result in stresses and are a cause of failure.